Manufacturing of spiral bevel and hypoid gears can be conducted in several ways. The following methods are among those commonly known:                1. Face hobbing with a circular face cutter, which rotates while the work also rotates (continuous indexing).        2. Face hobbing with tapered hob (peripheral cutter), which rotates while the work also rotates (continuous indexing).        3. Shaping method with one or two tools which move linearly while the work rotates (continuous or single indexing).        4. Face milling, with circular face cutter, which rotates while the work is not rotating (non-generating) or which rotates while work only performs a roll (generating), but no continuous indexing motion (single indexing).        5. Universal 5-axis milling with pencil shaped end mill (single slot manufacturing).        
In face milling (intermittent or single indexing) processes, tooth slots are formed individually in succession by feeding a rotating tool into a workpiece to a predetermined depth, withdrawing the tool, and indexing the workpiece to another (usually the next) tooth slot position. The steps of feeding, withdrawing and indexing are repeated until all tooth slots are formed. This type of face milling process is known as a non-generating process. The profile shape of a tooth on a workpiece is produced directly from the profile shape on the tool.
Alternative to non-generated face milling, a face milling generating process may be performed wherein once the tool is fed to a predetermined depth, the tool and workpiece are then rolled together in a predetermined relative rolling motion, known as the generating roll, as though the workpiece were rotating in mesh with a theoretical generating gear, the teeth of the theoretical generating gear being represented by the stock removing surfaces of the tool. The profile shape of the tooth is formed by relative motion of the tool and workpiece during the generating roll. The steps of feeding, rolling, withdrawing and indexing are repeated for each tooth slot until all tooth slots are formed.
In face hobbing (continuous indexing) processes (non-generated or generated), the tool and workpiece rotate in a timed relationship and the tool is fed to depth thereby forming all tooth slots in a single plunge of the tool. After full depth is reached, a generating roll may be performed.
The above methods 1-4 are well known and have been performed for more than 50 years. Method 5 became possible with the ability to enter complex free form surfaces into the computer control of 5-axis universal milling machines. While the manufacturing time is usually between about 100 and 1000 times that of the above processes 1-4 and the accuracy is in general less than that of the dedicated machines used to perform methods 1-4, the advantage of 5-axis bevel gear machining on a universal milling machine is the flexibility. No special cutting tool is required and the bevel gear size is only limited by the size of the 5-axis milling machines available.
On the universal milling machines, a spherical or cylindrical shaped mill is used in order to shape the tooth flank surfaces. The data post processing uses flank surface points and in some cases normal vectors to calculate the machining paths. The machining paths have to be sufficiently accurate so as to achieve enveloping paths which approximate the target surface with reasonable precision. The orientation of enveloping paths (flats) is only linked to the machining strategy, in order to minimize the machining time and the deviation from the target flank surface.